Waterproofing a bathroom floor before tiling: a step-by-step guide

What the waterproofing layer actually does, and where it's required

A waterproofing layer (Estonians usually call it niiskustõke) stops water that gets through tile joints from reaching the concrete screed, the floor structure, or the flat below. Grout and silicone are not waterproof on their own over time; they crack, shrink, and let moisture through. The membrane or liquid coating underneath is what actually does the job.

In a Tallinn flat, this matters most on the floor and in the shower area, extending at least 20 to 30 centimetres up the walls, and higher on the wall directly behind a shower head or bath tap, typically to about 2 metres. In an apartment building, a failed floor membrane is not just your problem: water finds its way to the ceiling of the flat below, and you're the one who pays for the repair.

Wooden houses in Kalamaja or Nõmme need this layer just as much, if not more, because the floor structure underneath is timber rather than concrete, and timber that gets wet repeatedly doesn't dry out the way concrete does. There is no version of a tiled bathroom floor where skipping this step is a reasonable shortcut.

What materials and tools you need to get hold of

Two waterproofing approaches are common for DIY work: a liquid two-component or one-component waterproofing coating applied with a brush or roller, or a membrane system with a fleece band at joints and corners. Liquid coatings are more forgiving for a beginner because there's less cutting and fitting involved; membranes give a more even thickness but need careful overlapping.

Alongside the waterproofing product itself, you'll need a primer suited to your substrate (concrete screed and old tile both need different primers, check the tin), corner and joint reinforcement tape or fleece strip, a notched or flat trowel or a paint roller depending on the system, a mixing bucket if it's a powder-based product, and a wide putty knife for smoothing corners.

Buy enough to do two full coats plus the corner reinforcement, and read the coverage rate on the tin rather than guessing; running out halfway through the second coat means an uneven layer once you resume. If you'd rather not source and match all of this yourself, our tiling service, from 35 € per job, includes the waterproofing as part of the floor preparation.

Order of work: from primer to the second coat

Start with a clean, dry, dust-free substrate. Vacuum thoroughly and check the screed is fully cured; a newly laid screed usually needs several weeks before it's ready for waterproofing, not days. Apply the primer evenly with a roller and let it dry fully, following the time given on the product.

Fit the corner and joint reinforcement tape first, before the main coat, pressing it into a thin layer of the waterproofing product at every internal corner, floor-to-wall junction, and around the drain. This is the detail that fails most often in amateur work, so take your time here rather than rushing to the broad areas.

Apply the first full coat across the floor and up the walls to the required height, working it into an even layer with no thin patches or missed spots, particularly at the wall-floor junction. Let it dry according to the product's instructions, then apply a second coat at right angles to the first, which helps cover any pinholes or thin spots left by the first pass.

Drying time and checking the work before tiling begins

Drying times vary by product, but a rough figure is 12 to 24 hours between coats and a further 24 to 48 hours before tiling, longer in a cold or poorly ventilated room. Estonian winters mean unheated bathrooms during renovation dry more slowly than the tin's figures, which are usually based on 20°C. Don't shortcut this by running a heater right next to the wall; even drying matters more than fast drying.

Before tiling, check the coating visually under a raking light for thin patches, pinholes, or missed corners. Run a hand over it once fully dry to feel for unevenness. Some liquid systems allow a simple flood test on the floor area, leaving water standing for a few hours to check the drain and joints hold; check whether your product and drain type support this before trying it.

Where amateurs most often go wrong

The single most common mistake is treating corner reinforcement as optional or an afterthought, applying it after the main coat instead of bedding it into a wet layer first. Corners and the floor-drain junction are where nearly all real leaks start, not the flat, open areas of the floor.

The second is not respecting drying times between coats, particularly in an unheated bathroom during a renovation done over a weekend. A coat that looks dry on the surface may still be curing underneath, and tiling too early traps moisture in the wrong place.

The third is applying the waterproofing too thin to save product, especially on walls, where gravity pulls the coating down as it's applied. A thin, patchy coat gives a false sense of security; it looks finished but doesn't perform as a barrier once tiles and grout go on top of it.

• Bed corner tape into a wet layer, never apply it dry afterwards
• Extend wall waterproofing 2 metres behind shower heads and taps
• Wait for full drying between coats, especially in cold rooms
• Apply two full coats at right angles, not one thick one
• Check the floor-drain junction carefully before tiling over it

When to leave waterproofing and tiling to a professional instead

If your bathroom is being reconfigured, if the drain needs moving, or if the floor build-up involves underfloor heating, the waterproofing sits in a more complex sequence with other trades and is worth having planned as one job rather than pieced together. That's the kind of work covered by our bathroom renovation service, from 3 500 € per job depending on scope.

If you've already tiled without waterproofing and are seeing damp patches, discolouration, or a musty smell, that's a sign water is already past the tiles, and the fix usually means lifting them rather than sealing over the top. This is worth a professional assessment before you spend more money on materials that won't solve the underlying problem.

Once tiling is done, the final line of defence at joints between floor and wall, and around the bath or shower tray, is a proper silicone seal rather than grout, which we offer from 45 € per job. And if electrical work such as a heated floor mat or new lighting is part of the plan, that stays with a qualified electrician, never a DIY job alongside wet-area waterproofing.